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    function error=cerror(y1,y2,label)
% CERROR Computes classification error.
%
% Synopsis:
%  error = cerror(y1,y2)
%  error = cerror(y1,y2,label) 
%
% Description:
%  error = cerror(y1,y2) returns classification error, i.e.,
%      error=  1/length(y1) sum_i L( y1(i), y2(i))
%
%    where L(a,b)=0 if a==b and L(a,b)=1 if a ~= b.
%
%    error = cerror(y1,y2,label) considers only labels
%    find(y2==label), i.e., if y1,y2 from {-1,1} then
%
%   false_positives_rate = cerror(y1,y2,-1)
%   false_negatives_rate = cerror(y1,y2,+1)
%
% Input:
%  y1 [1 x n] Vector of integers (response of classifier).
%  y2 [1 x n] Vector of integers (ground truth).
%  label [int] Selected label.
%
% Output:
%  error [real] Error. 
%
% Example:
%  classifier  = [+1,+1,+1,-1]
%  groundtruth = [-1,+1,-1,+1]
%  error = cerror(classifier,groundtruth)
%  false_pos = cerror(classifier,groundtruth,-1)
%  false_neg = cerror(classifier,groundtruth,1)
%
% See also 
%  ROC
%

% About: Statistical Pattern Recognition Toolbox
% (C) 1999-2003, Written by Vojtech Franc and Vaclav Hlavac
% <a href="http://www.cvut.cz">Czech Technical University Prague</a>
% <a href="http://www.feld.cvut.cz">Faculty of Electrical Engineering</a>
% <a href="http://cmp.felk.cvut.cz">Center for Machine Perception</a>

% Modifications:
% 09-jun-2004, VF
% 14-Jan-2003, VF

y1=y1(:);y2=y2(:);

if nargin < 3,
  error=length(find((y1-y2)~=0))/length(y1);
else
  inx = find(y2==label);
  error = length( find(y1(inx)~=label) )/length(y1);
end

return;